/// <summary>
/// Decrements the reference count for the singleton instance of the given type,
/// and calls its <see cref="IDisposable.Dispose"/> method if the reference
/// count gets to zero.
/// </summary>
/// <param name="type">The singleton instance's class type.</param>
/// <returns>
/// Returns true if the singleton instance's reference count drops to zero and
/// its <see cref="IDisposable.Dispose"/> method is called, otherwise returns false.
/// </returns>
public static bool Dereference(Type type)
{
//Since the singleton paradigm allows for only one instance of a
// particular type, we will use the type as a key to identify which
// singleton instance to return.
Type key = type;
IDisposableSingleton instance;
lock (SingletonManagementMutex)
{
//Add the reference counter key if it does not exist.
if (!SingletonInstanceReferenceCount.ContainsKey(key))
{
SingletonInstanceReferenceCount.Add(key, 1);
}
//Add the singleton instance key if it does not exist.
if (!SingletonInstances.ContainsKey(key))
{
SingletonInstances.Add(key, null);
}
//If the reference count is 0, dispose the singleton instance.
if (0 == (--SingletonInstanceReferenceCount[key]))
{
if (null != (instance = SingletonInstances[key]))
{
//Remove the reference from the singleton instance dictionary before disposing.
SingletonInstances[key] = null;
instance.DisposeWhenDereferenced();
return(true);
}
}
return(false);
}
}
/// <summary>
/// Gets the singleton instance of the specified class type that is managed
/// by <see cref="DisposableSingletonManager"/>. If no instance exists, then
/// one is created using the provided function or the type's parameterless contructor.
/// This method also increments the singleton instance's reference count so that
/// the instance's <see cref="IDisposable.Dispose"/> method is not called when there
/// are multiple references to the instance in existence.
/// </summary>
/// <param name="createInstance">
/// A function to create the singleton instance, or null to use its parameterless contructor.
/// </param>
/// <param name="type">The singleton instance's class type.</param>
/// <returns>Returns the singleton instance of the specified type.</returns>
public static IDisposableSingleton GetInstance(Func <IDisposableSingleton> createInstance, Type type)
{
//Since the singleton paradigm allows for only one instance of a
// particular type, we will use the type as a key to identify which
// singleton instance to return.
Type key = type;
lock (SingletonManagementMutex)
{
//Add the reference counter key if it does not exist.
if (!SingletonInstanceReferenceCount.ContainsKey(key))
{
SingletonInstanceReferenceCount.Add(key, 0);
}
//Add the singleton instance key if it does not exist.
if (!SingletonInstances.ContainsKey(key))
{
SingletonInstances.Add(key, null);
}
//If the reference count is 0, create a new singleton instance.
if (SingletonInstanceReferenceCount[key] == 0)
{
SingletonInstances[key] = CreateInstance(createInstance, type);
}
//Increment the reference count.
SingletonInstanceReferenceCount[key]++;
//Return the singleton instance.
return(SingletonInstances[key] as IDisposableSingleton);
}
}